1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery which has an improved structure in which charging and discharging improve the battery capacity.
2. Description of the Related Art
In general, secondary batteries capable of charging and discharging are applied to portable electronic apparatus such as cellular phones, notebook-type computers, computer camcorders and the like, and research into secondary batteries is being vigorously conducted.
In particular, secondary batteries are classified into a variety of batteries, including nickel-cadmium (Nixe2x80x94Cd) batteries, lead acid storage batteries, nickel metal hydride (Nixe2x80x94MH) batteries, lithium ion batteries, lithium polymer batteries, metal lithium batteries, air-zinc acid storage batteries, and the like.
Among the above-mentioned batteries, lithium batteries have a service life three times longer than Nixe2x80x94Cd batteries or Nixe2x80x94MH batteries and are in widespread use in terms of their excellent energy density per unit weight.
Lithium batteries are classified into liquid electrolyte batteries and polymer electrolyte batteries according to the type of electrolyte used. Generally, batteries using a liquid electrolyte are called lithium ion batteries and batteries using a polymer electrolyte are called lithium polymer batteries.
Lithium secondary batteries may have various shapes. Typically, cylindrical or prismatic batteries are fabricated to be used mainly as lithium-ion batteries. Lithium polymer secondary batteries have flexibility so that they are relatively free in view of shape design. Accordingly, lithium polymer secondary batteries having excellent safety and freedom in shape design and being light-weight are advantageous in attaining miniaturized and light-weight portable electronic apparatus, and research into the lithium polymer secondary battery is being carried out in various manners.
The above-described lithium polymer secondary battery is schematically shown in FIG. 1.
Referring to FIG. 1, the lithium polymer secondary battery includes an electrode assembly, a lower case 11 having a space 11a in which the electrode assembly is accommodated, and an upper case 12 for hermetically closing the space 11a of the lower case 11. One side periphery of the upper case 12 is connected to the lower case 11.
The electrode assembly has positive electrode plates 13 and negative electrode plates 14 stacked sequentially, with separators 15 interposed therebetween. A positive electrode tab extends from the positive electrode plate 13 at one side thereof and a negative electrode tab extends from the negative electrode plate 14 at one side thereof. A plurality of positive electrode tabs at the positive electrode plates 13 are mutually welded to form a positive electrode tab group 16. Also, a plurality of negative electrode tabs drawn out from the negative electrode plates 14 in the same direction are mutually welded to form a negative electrode tab group 17. A positive electrode terminal 18 and a negative electrode terminal 19 are welded to the positive and negative electrode tab groups 16 and 17, respectively, to then be drawn outside the upper and lower case values 11 and 12.
In the lithium polymer secondary battery having the above-described configuration, the upper and lower cases 11 and 12 which are Al multi-film pouches, are formed of various materials such as nylon, polyethylene (PE), aluminum (Al), ethyl acetic acid (EAA), polyethylene terephthalate (PET), polypropylene (PP) and the like. An electrolytic solution is injected into the upper and lower cases 11 and 12 and then the electrode assembly is installed therein. In this case, when the electrode assembly is inserted into the upper and lower cases 11 and 12 and then the upper and lower cases 11 and 12 are sealed, the electrolytic solution sticking to the portions of the positive electrode tab group 16 and the negative electrode tab group 17 stick to the sealing portions at the peripheries of the upper and lower cases 11 and 12, which results in a sealing strength that is insufficient.
As shown in FIG. 1, the positive electrode terminal 18 made of Al and the negative electrode terminal 19 made of Cu or Ni which protrude outside the upper and lower cases 11 and 12 must be folded to be connected to a terminal (not shown) of a battery pack. However, in this case, the positive and negative electrode terminals 18 and 19 may contact the upper or lower case 11 or 12 in a direction in which the positive and negative electrode terminals 18 and 19 are folded, thereby undesirably causing shorts in the battery.
To solve the above problems, it is an object of the present invention to provide a secondary battery having improved safety and productivity, by preventing an electrolytic solution from sticking to the sealing portion of a case and preventing a short-circuiting from occurring due to contact between the case and terminals protruding outside the case.
Accordingly, to achieve the above object, there is provided a secondary battery including an electrode assembly formed by sequentially stacking positive electrode plates each having a positive electrode tab formed at one side thereof, negative electrode plate each having a negative electrode tab formed at one side thereof, and separators interposed between the positive electrode plates and the negative electrode plates, for insulating the positive and negative electrode plates from each other, the positive electrode tabs being welded to each other to form a positive electrode tab group, and the negative electrode tabs being welded to each other to form a negative electrode tab group, a case having a lower case part having a space in which the electrode assembly is accommodated, and an upper case part connected to one side periphery of the lower case part and fixed to the lower case part, for hermetically sealing the space of the lower case part, the upper case part and the lower case part having sealing portions at the peripheries thereof to be sealed to each other, a positive electrode terminal welded to the positive electrode tab group, the positive electrode tab group being supported in the sealing portion and protruding outward from the case, a negative electrode terminal welded to the negative electrode tab group, the negative electrode tab group being supported in the sealing portion thereof and protruding outward from the case, and short preventing means provided between the positive and negative electrode terminals and the case in a direction in which the terminals are folded.
In an embodiment of the present invention, the short preventing means,is an insulating member fixed to the positive electrode terminal and the negative electrode terminal.
In still another embodiment of the present invention, the short preventing means is an insulating member fixed to the front sidewall of the case.
Also, in another embodiment of the present invention, the short preventing means is a supporting portion formed by protruding the sealing portion outward from the case to support the positive and negative electrode terminals.
According to another aspect of the present invention, there is provided a secondary battery including an electrode assembly formed by sequentially stacking positive electrode plates each having a positive electrode tab formed at one side thereof, negative electrode plate each having a negative electrode tab formed at one side thereof, and separators interposed between the positive electrode plates and the negative electrode plates, for insulating the positive and negative electrode plates from each other, the positive electrode tabs being welded to each other to form a positive electrode tab group, and the negative electrode tabs being welded to each other to form a negative electrode tab group, a case having a lower case part having a space in which the electrode assembly is accommodated, and an upper case part connected to one side periphery of the lower case part and fixed to the lower case part, for hermetically sealing the space of the lower case part, the upper case part and the lower case part having sealing portions at the peripheries thereof to be sealed to each other, a positive electrode terminal welded to the positive electrode tab group, the positive electrode tab group being supported in the sealing portion and protruding outward from the case, a negative electrode terminal welded to the negative electrode tab group, the negative electrode tab group being supported in the sealing portion thereof and protruding outward from the case, and an electrolytic solution blocking member which envelops the electrode assembly.
The electrolytic solution blocking member is preferably a film envelop made of one material selected from the group consisting of polyethylene (PE), polyvinyl carbonate (PVC), hexafluoropropylene (HFP) and a mixture of polyvinylidene fluoride (PVDF) and HFP.
Here, short preventing means may be further provided between the positive and negative electrode terminals and the case in a direction in which the terminals are folded.